HABITS OF KOALA 143 The tooth formula of the genus is I -f- C -J- Pm ^- M ^-J-y. The additional lower molar seems to "be exceptional, and has been found in one specimen only. In the alimentary tract the most remarkable structure is the large intestine, which is very capacious for the first 28 inches 01 so of its course. This section of the colon is lined with rugae precisely like those which are found in the caecum. These folds which at first are some twelve in number, fuse lower down, anc by the time that the colon approaches the external orifice are reduced to five. Similar folds, as already stated, occur in the caecum, but do not extend as far as its blind end. The caecuir is proportionately and actually larger than in any other Marsupial The gall-bladder is unusually elongated. The Koala is mainly crepuscular or nocturnal in its habits. 11 feeds so exclusively upon the leaves of the gum-tree (JEu FIG. 70.—Koala. PJiascoZarctos cinereus. that it is impossible to keep the creature long in captivity ii lands where that particular kind of food is not available. The female, though she seems to bear but a single young one which is carried on. the back after the fashion of some Opossums has two nipples. The animal's slow habits seem to require * nocturnal and retired life. It is about as. lethargic as tin Sloth, and it is said to further resemble that animal in clingin| firmly to a branch even after it is sliot.